Manufacture of cellulose triacetate textile materials



y 1961 J. DOWNING 2,982,598

MANUFACTURE OF CELLULOSE TRIACETATE TEXTILE MATERIALS Filed Dec. 5, 1956 FIG.|

4 HIM Critical Humidity (grains per cubic foot) N U- 0 IO 20 3O 4O 5O 6O 3 Temperuhlre C INVENTOR BY M 44 M1 ATTORNEY United States Patent MANUFACTURE OF CELLULOSE TRIACETAT TEXTILE MATERIALS Filed Dec. 5, 1956, Ser. No. 626,515 Claims priority, application Great Britain Dec. 12, 1955 6 Claims. (CI. 18-54) This invention relates to the manufacture of filamentary materials of cellulose triacetate by the dry spinning method. The term cellulose triacetate is used to denote cellulose acetates of acetyl value above 59% reckoned as acetic acid. Preferably cellulose acetates of acetyl value above 60% are used. i

It is known that cellulose triacetate yarns can be made by extruding a solution of the cellulose triacetate in methylene chloride, or better in a mixture of methylene chloride and methanol or ethanol containing 88% by weight or more of methylene chloride, into an evaporative medium through a spinning jet containing a number of orifices, and collecting the filaments so formed as a single yarn. While excellent products can be obtained in this way, difliculty is sometimes found in securing stable spinning over long periods; in particular partial or even complete fusion between filaments frequently occurs and has sometimes proved very difiicult to prevent.

It has now been found that filament fushion can be completely or nearly completely prevented if the absolute humidity of the evaporative medium, at least .in the neighbourhood of the point of extrusion, is adjusted to a value below a critical maximum which varies to some extent with the temperature maintained in the spinning cell, but is always below S, and preferably below 4.7,.

grains/cubic foot. 1 i

According to the invention therefore filamentary materials of cellulose triacetate are made by extruding a solution of the cellulose triacetate in methylene chloride, or better in a mixture of methylene chloride and methanol or ethanol containing at least 88% byweight fof methylene chloride, into an evaporative medium whose absolute humidity, at least in the neighborhood of the point of extrusion, is adjusted to a value below a critical maximum which is linearly related to the average temperature of the evaporative medium surrounding the filaments from the point of extrusion to the point at which they are substantiallyfully set, being 4.7 grains/ cubic foot .at 48 C. and 3 grains/ cubic foot at 28 C.,- subject to anoverriding maximum of andpreferably 4.7 grains/cubic foot. For the purpose of the present specification'the average temperature of the evaporative medium is taken as the mean of 'the temperature just below the point of extrusion and the temperature at the point where the filaments become substantially fully set, i.e. when their.

solvent content has fallen low enough to allow them to be handled without damage. Preferablythe humidity is below the critical maximum over the whole of the path' followed by the filaments before they are fully set.

By means of the invention it becomes readily possible:

to obtain cellulose triacetate yarns which are not only free from fused or cohering filaments, but also have a very useful textile product (tenacityxextensibility) even when the spinning cell is not directly heated, though when it is convenient to'heat the cell it may be found possible to obtain yarns of yet higher tenacity or extensibility. When the cell is not heated the spinning solution is best extruded at a temperature above 40 C. and

especially above 50 C., e.-g. 55-85 C. Even when the;

cell is heated it is preferable also to heat the spinning solution; for example when the cell is so heated thatthe average temperature of the evaporative medium is about 40-50 C. or above, the spinning solution may also be at a temperature within this range or at a higher temperature. In all cases it is best that the temperature of the evaporative medium immediately below the point of extrusion should not exceed40 C., and it may with advantage be lower, especially about 24-35 C. The concentration of the cellulose triacetate in the spinning solution will usually be between 17 and 27%, depending on its viscosity inthe known Way.

In ordinary dry spinning practice the spinning solution is extruded downwardly into the spinning cell through which flows a current of the evaporative medium, usually air. It is convenient to provide near the top of, the cell an opening through which air can be drawn from the atmosphere in the spinning room, and to extract solvent vapour-laden air by suction from the bottom of the cell. This is obviously a desirable procedure, since it does not call for any special means for supplying the evaporative medium.

We have found that the advantages accruing from the present invention can be obtained without losing more than a small part of the economic benefits of the above method of working, by introducing a relatively small proportion of specially conditioned air 'or other evaporative medium into the spinning cell near or above the spinning,

7 if the humidity of the conditionedair is too high for this,"

provided its humidity is below the critical and it is concentrated round the spinning jet.

A preferred method of carrying out the invention involves feeding the conditioned air into the spinning cell close to the spinning jet and at a level above that of the jet face, while the air from the surroundingatmosphere' enters the cell through one or more openings in the cell wall at a level somewhat below that of the jet face,

especially between about 2 and'8 inches below. For ex ample, the conditioned air may enter the cell through equally spaced openings in an annular distributor sur' rounding the jet or above and coaxial with the jet. By

this means the conditioned air is concentrated round the spinning jet and also to some extent round the filaments immediately after their formation, after which it rapidly becomes uniformly mixed with the unconditioned airsasit passes down the cell. i

'However low the humidity of the conditioned air,'it

is preferable that the amount employed should be as least 10% and preferably 15% or more, e.g'. 15-30%,of the total amount of air drawn through the cell. i A formof dry spinning device which may be used for carrying out the process 'of the invention is illustratedin the accompanying drawing, in which the figure isga side view in section of the device. i T i s r Y Referring now to Figure 1, the dry spinning device comprises a vertical tubular spinning cell 1 which .may,

(though it neednot) be provided with a heating jacket '2.

having an inlet 3 and outlet 4 for a heating fluid." The upper end of the cell is provided with a closure 5, and l the bottom with a conical end piece '6 leadinglto a gas, lead-off 7 through which air laden withsolventvapour;

can be drawn away from the cell. In one side of the cell near its lower end is a small opening 8 which a yarn 9 formed in the cell can be drawn from it after passing round a guide 10.

,From the top of the cell a feed tube 11 for spinniug solution leads to a spinning jet 12, and around the feed tube a little above the jet is an annular distributor 13 havingequally spaced holes 14 opening downwardly into the cell, and connected by a pipe 15 to a source of conditioned air (not shown). Some 6 inches below the face of the jet 11 isan opening 16 in the cell wall through which air can be drawn from the surrounding atmosphere.

Fig. 2 of the drawings shows in graphical form the relation between the critical maximum humidity and the temperature of the air in the vicinity of the point of extrusion of the filaments. The line A, B, C represents the relation when the overriding maximum is grains per cubic foot and the line A, D, E the relation when the overriding maximum is 4.7 grains per cubic foot.

The invention is further illustrated by the following examples.

Example I A dry spinning cell of the type described by reference to the drawing was used. The cell was provided with a heating jacket, and under operating conditions the temperature in the cell averaged about 47 C. The spinning solution was a 21% solution of cellulose triacetate in a methylene chloride/ methanol mixture containing 90% by weight of methylene chloride, and it was extruded at a temperature of 47 C. through a spinning jet containing 84 holes each of diameter 0.05 mm. Air was extracted from the bottom of the cell at a rate of cubic feet per minute, and conditioned air at a temperature of 30-31 C. and a humidity of 2.7 grains/cubic foot was supplied through the annular distributor at a rate of 2 cubic feet per minute. The air in the spinning room was at 26.5 C., and had a humidity of 5.1 grains/cubic foot. The average humidity of the air passing through the spinning cell was thus 4.6 grains/cubic foot. Stable spinning was easily achieved, with no trace of filament fusion. If the humidity of the conditioned air was made equal to that of the spinning room air it became quite impossible to prevent a serious amount of filament fusion.

Example 11 The process of Example I was repeated,.except that the spinning cell was not heated, all the air employed as the evaporative medium was supplied through the annular distributor 13 at a humidity of 2.4 grains/cubic foot and a temperature of 25 C., and the spinning solution was at a temperature of 60 C. Again there was no trace of filament fusion.

By working in accordance with both the above examples yarns could be produced having tenacities of about 1.1-1.3 grams per denier, and extensibilities of about 20-24%.

Having described my invention, what I desire to secure by Letters Patent is:

1. In a process for the manufacture of cellulose triacetate filamentary materials by dry spinning wherein a solution of the cellulose triacetate in a solvent consisting of 88-100% by weight of methylene chloride and 12-0% by weight of an unsubstituted monohydric alcohol having at most two carbon atoms in the molecule is extruded into a current of air over a period during which the absolute humidity of the ambient air exceeds a hereinbelow defined critical maximum at least a portion of the time, the improvement which comprises adjusting the absolute humidity of the evaporative medium in the neighbourhood of the point of extrusion to a value of at most said critical maximum which is linearly related to the average temperature of the air surrounding the filaments from the point of extrusion to the point at which they are substantially fully set, being 4.7 grains/cubic foot at 48 4 C. and 3 grains/cubic foot at 28 C., subject to an ovcrriding maximum of 5 grains/cubic foot.

2. In a process for the manufacture of cellulose triacetate filamentary materials by dry spinning wherein a solution of the cellulose triacetate in a solvent consisting of 88-100% by weight of methylene chloride and 12-0% by weight of an unsubstituted monohydric alcohol having at most two carbon atoms in the molecule is extruded into a current of air over a period during which the absolute humidity of the ambient air exceeds a hereinbelow defined critical maximum at least a portion of the time, the improvement which comprises adjusting the absolute humidity of the evaporative medium in the neighbourhood of the point of extrusion to a value of at most said critical maximum which is linearly related to the average temperature of the air surrounding the filaments from the point of extrusion to the point at which they are substantially fully set, being 4.7 grains/cubic foot at 48 C. and 3 grains/cubic foot at 28 C., subject to an over-riding maximum of 4.7 grains/cubic foot, the said adjustment being effected by feeding conditioned air having a humidity of at most the said critical maximum, having regard to the average temperature of the evaporative medium, into the vicinity of the point of extrusion and at a level at least as high, and also drawing air from the surrounding atmosphere into the path followed by the filaments at a level 2-8 inches below the point of extrusion, the amount of the conditioned air being at least 10% of the total amount of the conditioned air and the air drawn from the surrounding atmosphere.

3. In a process for the manufacture of cellulose triacetate filamentary materials by dry spinning wherein a solution of the cellulose triacetate in a solvent consisting of 88-100% by weight of methylene chloride and 12-0% by weight of an unsubstituted monohydric alcohol having at most two carbon atoms in the molecule is extruded into a current of air over a period during which the absolute humidity of the ambient air exceeds a hereinbelow defined critical maximum at least a portion of the time, the improvement which comprises adjusting the absolute humidity of the evaporative medium in the neighbourhood of the point of extrusion to a value of at most said critical maximum which is linearly related to the average temperature of the air surrounding the filaments from the point of extrusion to the point at which they are substantially fully set, being 4.7 grains/cubic foot at 48 C. and 3 grains/cubic foot at 28 C., subject to an over-riding maximum of 4.7 grains/cubic foot, the said adjustment being effected by feeding conditioned air at a temperature of 24 -35 C. and having a humidity of at most the said critical maximum, having regard to the average temperature of the evaporative medium, into the vicinity of the point of extrusion and at a level at least as high, and also drawing air from the surrounding atmosphere into the path followed by the filaments at a level 2-8 inches below the point of extrusion, the amount of the conditioned air being 15-30% of the total amount of the conditioned air and the air drawn from the surrounding atmosphere.

4. In a process for the manufacture of cellulose triacetate filamentary materials by dry spinning wherein a solution of the cellulose triacetate in a solvent consisting of 88-100% by weight of methylene chloride and 12-0% by weightof an unsubstituted monohydric alcohol having at most two carbon atoms in the molecule is extruded at a temperature above 50 C. into a current of air in an unheated spinning cell over a period during which the absolute humidity of the ambient air exceeds a hereinbelow defined critical maximum at least a portion of the time, the improvement which comprises adjusting the absolute humidity of the evaporative medium in the neighbourhood of the point of extrusion to a value of at most said critical maximum which is linearly related to the average temperature of the air surrounding the filaments from the point of extrusion to the point at which they are substantially fully set, being 4.7 grains/cubic foot at 48 C. and 3 grains/cubic foot at 28 C., subject to an over-riding maximum of 4.7 grains/cubic foot, the said adjustment being effected by feeding conditioned air having a humidity of at most the said critical maximum, having regard to the average temperature of the evaporative medium, into the vicinity. of the point of extrusion and at a level at least as high, and also drawing air from the surrounding atmosphere into the path followed by the filaments at a level 2-8 inches below the point of extrusion, the amount of the conditioned air being 1530% of the total amount of the conditioned air and the air drawn from the surrounding atmosphere.

5. In a process for the manufacture of cellulose triacetate filamentary materials by dry spinning wherein a solution of the cellulose triacetate in a solvent consisting of 88100% by weight of methylene chloride and 12-0% by weight of an unsubstituted monohydric alcohol having at most two carbon atoms in the molecule is extruded at a temperature within the range of 4050 C. into a current of air in a spinning cell heated to.a temperature within the range 40-50 C. over a period during which the absolute humidity of the ambient air exceeds a hereinbelow defined critical maximum at least a portion of the time, the improvement which comprises adjusting the absolute humidity of the evaporative medium in the neigrbourhood of the point of extrusion to a value of at most said critical maximum which is linearly related to the average temperature of the air surrounding the filafoot and 48 C. and 3 grains/cubic foot at 28 0., subject to an over-riding maximum of 4.7 grains/cubic foot, the said adjustment being effected by feeding conditioned air having a humidity of at most the said critical maxi-i ments from the point of extrusion to the point at which 1 they are substantially fully set, being 4.7 grains/cubic mum, having regard to the average temperature of the evaporative medium, into the vicinity of the point of extrusion and at a level at least as high, and also drawing air from the surrounding atmosphere into the'path followed by the filaments at a level 2-8 inches below the point of extrusion, the amount of the conditioned air. being 15-30% of the total amount of the conditioned air and the air drawn'from the surrounding atmosphere.

6. Process in accordance with claim 1 wherein said over-riding maximum is 4.7 grains/cubic foot.

References Cited in the file of this patent UNITED STATES PATENTS 838,758 Thiele Dec. 18, 1906 2,057,141 Eickengrun Oct. 13, 1936 2,387,791 Hoflman Oct. 30, 1945 2,396,165 Ernsberger Mar. 5, 1946 2,402,942 Bludworth July 2, 1946 2,515,393 Burke July 18, 1950 2,542,301 Barrington Feb. 20, 1951 2,657,973 Johnson Nov. 3, 1953 2,692,405 Gayle: Oct. 26, 1954 

1. IN A PROCESS FOR THE MANUFACTURE OF CELLULOSE TRIACETATE FILAMENTARY MATERIALS BY DRY SPINNING WHEREIN A SOLUTION OF THE CELLULOSE TRIACETATE IN A SOLVENT CONSISTING OF 88-100% BY WEIGHT OF METHYLENE CHLORIDE AND 12-0% BY WEIGHT OF AN UNSUBSTITUTED MONOHYDRIC ALCOHOL HAVING AT MOST TWO CARBON ATOMS IN THE MOLECULE IS EXTRUDED INTO A CURRENT OF AIR OVER A PERIOD DURING WHICH THE ABSOLUTE HUMIDITY OF THE AMBIENT AIR EXCEEDS A HEREINBELOW DEFINED CRITICAL MAXIMUM AT LEAST A PORTION OF THE TIME, THE IMPROVEMENT WHICH COMPRISES ADJUSTING THE ABSOLUTE HUMIDITY OF THE EVAPORATIVE MEDIUM IN THE NEIGHBOURHOOD OF THE POINT OF EXTRUSION TO A VALUE OF AT MOST SAID CRITICAL MAXIMUM WHICH IS LINEARLY RELATED TO THE 